Imaging devices such as imaging sensor systems typically include an imaging sensor, and optics through which the optical path from the viewed scene passes to reach the imaging sensor. The optics serve to provide the desired focal length and field of view of the scene, and to focus the image onto the imaging sensor. In some applications, it is desirable that the optical system selectively provide two or more fields of view, such as a wide-angle field of view for general searching of a large area, and a narrow-angle field of view for higher-magnification, more-specific analysis of a small portion of the scene that is found to be of interest.
The imaging sensor may be selected for viewing any desired wavelength range, and imaging sensors are known for use in different wavelength ranges. Such wavelength ranges include, for example, wavelengths in the visible, the near infrared, the medium-wavelength infrared, and/or the long-wavelength infrared. Infrared sensors are typically cooled to cryogenic temperatures for optimal performance. The optics of the imaging sensor system must be compatible with the cold shielding required by the sensor, when such a cryogenic sensor is used.
In an application of interest, an imaging device requires imaging in two or more fields of view, with a straightforward approach for switching between the two fields of view. The imaging must be accomplished in two or more infrared wavelength ranges using a sensor that is cooled to the cryogenic range. Although it is conceivable to move the imaging sensor along the beam path when the field of view is switched, it is far preferable that both the focal surface of the optics and the cold stop of the cryogenic shielding remain at a fixed location when the field of view is switched. The imaging sensor, the cooling structure, and the associated cold stop may therefore remain at a fixed location along the beam path. No such imaging device is currently available, and there is a need for such an imaging device. The present invention fulfills this need, and further provides related advantages.